My guess is that you window is only attached to one of the spring loaded carriers.
I would suggest tilting and removing the sash from the frame. Look in the tracks on each side for the spring loaded carriers. One of them might be stuck, or it may have slipped and retracted upwards. This is difficult to explain, but those carriers have a slot in them where the pin on the bottom of the sash goes in. When you tilt the window, the carrier will have a slotted metal piece, kind of like the head of a screw, which will be parallel to the track of the window frame. In that position, the carrier should not move. When you put the sash back in the frame, and tilt it back in, those screw heads turn and free the carriers so that they can move up and down.
If one of your carriers has retracted, you would use a screwdriver to turn the screw head to the position where the carrier will move, and, with the screwdriver in the slot, pull the carrier down to the same level as the other carrier. Then turn that screw head to lock that carrier in position. Re-install the sash, and the window should work normally.
I also use a dry spray lubricant or a silicone spray on the window tracks and carriers once every couple of years.
If this is not your issue, please post some pictures of the window, and track with the sash in the normal position, and with the sash tilted.
If you have spiral balances (a tube in the track above each sash), you will need a special tool to fix it.
